Telephone protective system



p 17, 1929- c. LE G. FORTESCUE TELEPHONE PROTECTIVE SYSTEM Filed Aug. 8, 1927 Ii I 1|: Ill}: 1- .1 I I i I. I ii! J M W m M A W M a u Z n n w w [IA/W M e 6 7 n Mg 6. n W b u L7 mm 5 u m w Y my n if g (K K\ n 2 n n k n w 3 n u 8 D n 2 n m V? m m r11|||||||lswlllfillallrlliin r||||||||||4||1|||||||L INVENTOR Char/6's Led For/65cm? ATTdRNEY Patented Sept. 17, 1929 f j jomrso v STATES PATENT, OFFICE 35 ;preferred form.

s'YLvANIa cameras LE 0. rom'escun, or rrr'rsnumn, rsnnsnvamn, ASSIGNOR T ES Incnousn nmcrnrc & MANUFACTURING comm, A conrom'rron or rams- TELEPHONE PROTECTIVE SYSTEM Application filed August 8, 1927. Serial No. 211,433.

-My invention relates to telephone protective systems, and it has particular relatron toiapparatus for preventing an excessrve r se in voltage as a result either of inductlve 1nterference from power transmission lines or ,lightningdischarge in a telephone system.

-, Ina telephone system which parallels a powerline, it frequently happens that very considerable voltages are induced in the telephone lines by currents flowing in the power line. -Although these voltages may produce very little current in the telephone circuit, because the voltages are equalan-d opposite in the telephone circuit formed by the two ;wires, nevertheless potentials may be electromagnetically induced, which are quite -dangerous to persons handling the telephones. Furthermore, the telephone lines maybe subjected to lightning discharges which always introduce a very serious hazard to; persons coming in contact with thetelephone apparatus;

It is the object of my invention to overcome the difficulties just mentioned and to provide a safe protective system under very severe operating con-dltlons.

, Withthe foregoing and other objects: in view, which will be understood as the deseriptionproceeds, my invention consists in thejcircuits and apparatus described and claimed in the following specification and illustrated in the drawing, the single figure of which is a diagrammatical view of circuits and apparatus embodying my invention in a ,As shown in the drawing, my invention consists in a telephone circuit or apparatus 1, ,to-beprotected, which is connected to a twoconductor incoming line 2 by means of two protective panels 3 and 4. The incoming line 2 is subjected, not only to exposure to lightning discharges, but also toinductive interference from a power line 5, such as a sixty-circle line disposed parallel to the telephone line.

Thetelephone set to be protected, as inv,dicate-d at 1, is connected to the incomi ngline 2 by means of an equalizing reactor or inductance device 6, comprising two 50..$Qi,1s .7, and 8, one coil being in series with each line wire, said coils being substantlally non-inductive as to e ual and opposite currents fiowin in t e telephone c1rcu1t but offering an Inductance of about 8 henrles to the flow of in-phase currents in the two line wires of the telephone circuit. A drainage coil, or shunt-reactance device, 9, is also connected across the two conductors of the telephone circuit at a point nearest to the telephone set or other apparatus to be protected, said shunt-reactance device comprising two drainage coils l1 and 12 which are connected between the respective wires and ground, and which are non-induc tive as to equal currents simultaneously discharging in the same direction from the two line wires.

Thus, the series inductor 6 imposes large impedance to the induced -cycle currents, and the shunt inductor 9 offers a low impedance to such in-phase currents as pass through the series inductor, whereas the shunt-connected drain coils impose a high reactance with respect to oppositely flowing currents in the telephone circuit.

Blocking condensers 13 and 14, which may be of 10 microfarads capacity, are included in circuit with the drainage coils 11 and 12 for the purpose of preventing the shortcircuiting of the direct current commonly utilized in the telephone system.

Connected to the telephone lines between the series and shunt inductors 6 and 9 are a pair of multiple-electrode vacuum-discharge tubes 16 and 17, which eflect an excess-voltage connection between the respective line Wires and the ground, the specific form of the vacuum-tube arrester being the subject matter of an application of James L. McCoy, Serial N 0. 78,113, filed December 29, 1925, now Patent Number 1,649,035, dated November 15, 1927, and assigned to the Westinghouse Electric and Manufacturing Company.

The vacuum-tube arresters 16 and 17 are characterized by having a very quick response to excess-voltage conditions, but having a low breakdown voltage of the order of 350 volts and having a low momentary discharge current capacity of the order oi. a few amperes. Preferably low-voltage, low-current fuses 18 and 19 are interposed in the line conductors between the two vacuum-tube arresters 16 and 17.

Disposed across the line end of the series equalizing reactor 6 are a plurality of arc-gap discharge devices 20, which may comprise three knurled cylinders 21, of perhaps one inch diameter, spaced closely from each other, the center cylinder being grounded, and the end cylinders being connected to the respective line wires, the breakdown voltage of the two gaps being of the order of 3,000 volts.

The combination just described thus limits the induced sixty-cycle power current that can flow past the series reactor 6 to one ampere, which means that the voltage drop across the eight-henry inductance, at sixty cycles, will .be about 3000 volts, or enough to break down the gap-discharge devices 20, which are of a high current capacity, capable of shunting the discharge from 'the low-voltage discharge devices 16 and 17 A heavy discharge across the cylindrical gap devices 21 will result in the blowing of two high-voltage five-ampere fuses 23 and 24, which are connected in the respective line Wires between the incoming line 2 and the gap-discharge devices. Connected on the line side of the fuses 23 and 24 are two horngap devices 25 and 26, which have a breakdown voltage somewhat higher than the cyhndrical gap-discharge devices 20, and .which are discharged as soon as the fuses 23 and 24 blow, thereby by-passing current from the high-voltage fuses and the cylindrical gapdischarge devices, which are not self-clearing, and effectually clearing the line.

When it is realized that induced sixty-cycle voltages of the order of 1,000 volts must sometimes be handled under emergency conditions, and that lightning-discharge voltages of much greater magnitude must also be handled, it will be understood that the problem of affording any real protection to persons handling the telephone set is one of major importance, and the apparatus herein described has been found to be extremely effective for that purpose.

When the horn-gap devices 25 and 26 discharge, the resulting arcs are very heavy, and it has been found expedient, therefore, to divide the apparatus into two panels, placing the horn gaps, high-voltage fuses, cylindrical gaps and equalizing reactor on one panel 3, which is connected to the incoming line 2, and mounting the rest of the apparatus on a second panel 4, which is connected to the desk telephone set to be protected.

It has been found, in practice, that the apparatus as hereinabove described is quite necessary to give the full portection which must be provided in order to safeguard the lives of people who must handle the telephone apparatus indicated by the lines 11.

While I have described my invention in a preferred form, it will be understood that modifications and substitutions may be resorttherefore, that the appended claims shall be accorded the broadest construction consistent with their language and the prior art.

I claim as my invention:

1. An excess-voltage protective system comprising an apparatus to be protected, an incoming line connected thereto, an inductance device serially connected in said line, a low-voltage, low-current discharge device connected between said line and ground on the apparatus side of said inductance device, and a high-voltage, high-current discharge device connected between said line and ground on the line side of said inductance device.

2. A communication line subject to inductive interference from a commercial-frequency power line, communicating apparatus connected thereto, an inductance device serially connected in said line a low-voltage, low-current discharge device connected between said line and ground on the apparatus side of said inductance device, and a highvoltage, high-current discharge device connected between said line and round on the line side of said inductance device, the impedance of said inductance device to said induced commercial-frequency currents, multiplied by the momentary current-carrying capacity of said low-current discharge device, being higher than the breakdown voltage of said high-current discharge device.

3. A communication line subject to inductive interference from a commercial-frequency power line, communicating apparatus connected thereto, an inductance device serially connected in said line, a low voltage, low-current discharge device connected between said line and ground on the apparatus side of said inductance device, a high-voltage,

high-current discharge device connected between said line and ground on the line side of said inductance device, the impedance of said inductance device to said induced commercial-frequency currents, multiplied b the momentary current-carrying capacity 0 said low-current discharge device being higher than the breakdown voltage of said high-current discharge device, said high-current discharge device being of an arcing type which is incapable of interrupting its are, a hi hvoltage fuse between said last-mentioned ischarge device and the line, and a horn gap on the line side of said fuse and adapted to shunt out the are at said fuse when it blows.

4. A protective system comprising an apparatus to be protected, an incoming twowire line connected thereto, a series inductance device comprising two coils, one in series with each line-wire, said coils being substantially non-inductive as to equal and opposite currents flowing in the line-wires, lowcurrent protective means connected between said line-wires and ground at the apparatus end of said inductancedevice, and high current-capacity protective means connected between said line-wires and ground at the line end ofsaid series inductance device.

5. A communication-circuit protective system. comprising apparatus to be protected, an incoming two-wire line connected thereto, a series inductance device comprising two coils, one in series with each line-wire, said coils being substantially non-inductive as to equal and oppositeicurrents flowing in the communication-circuit, a shunt inductance device comprising two coils connected between the respective line-wires and ground at a point between said series inductance device and the apparatus to be protected, said last-mentioned coils being non-inductive as to equal currents simultaneously discharging in the same direction from the two line-wires, lowvoltage, low-current, excess-voltage protective means connected between said line-wires and ground at a pointbetween the two inductance devices, and high current-capacity protective means connected between said linewires and ground at the line end of said series inductance device.

In testimony whereof, I have hereunto sub scri lped my name this 6th day of August, 192 K CHARLES LE G. FORTESCUEQ 

